DEVELOPMENT OF A GENERAL DYNAMIC HYSTERETIC …With some modifications on the nailed wood joint model, a super shear wall model was developed, which describes the behavior of a whole

DEVELOPMENT OF A GENERAL DYNAMIC HYSTERETIC LIGHT-FRAME

STRUCTURE MODEL AND STUDY ON THE TORSIONAL BEHAVIOR OF OPEN-

FRONT LIGHT-FRAME STRUCTURES

By

JIAN XU

A dissertation submitted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY IN CIVIL ENGINEERIING

WASHINGTON STATE UNIVERSITY Department of Civil & Environmental Engineering

DECEMBER 2006

To the Faculty of Washington State University:

The members of the Committee appointed to examine the dissertation of JIAN XU find it satisfactory and recommend that it be accepted.

___________________________________ Chair ___________________________________ ___________________________________

___________________________________

___________________________________

ii

ACKNOWLEDGMENT

My advisor, committee chair, Dr. J. Daniel Dolan, made all research purposes

clear, had all research tools and testing data available, and made everything easier for me.

Without his guidance and encouragement, this dissertation would not have been possible.

I am especially thankful for his lenience and patience. Thank you for being such a

wonderful advisor.

Further acknowledgement is extended to Dr. William F. Cofer, Dr. David Pollock,

Dr. David McLean, and Kelly Cobeen for serving on my committee and providing

warmhearted support. I also thank all the persons that gave me help and encouragement

during this exceptional research journey.

I am especially indebted to my parents and my wife for their abiding love. This

dissertation is dedicated to them.

iii

Development of a General Dynamic Hysteretic Light-frame Structure Model and Study

on the Torsional Behavior of Open-front Light-frame Structures

Abstract

by Jian Xu, Ph.D.

Washington State University December 2006

Chair: James D. Dolan

Open-front light-frame structures may have significant torsional problems when

attacked by intense earthquakes. Full-size testing is a good tool to be employed to

understand their performance under significant seismic events, but it is limited due to the

high expense. So, a model, which is able to accurately represent the hysteretic dynamic

performance of light-frame structural systems under lateral loads is in demand.

All previous testing showed that the hysteretic behavior of nailed wood joints

governs the response of many wood systems when subjected to lateral loadings.

Unfortunately, commercially available software does not have an appropriate hysteretic

element for a nailed wood joint, and the accuracy and versatility of previously developed

nail joint elements are not satisfactory. A general hysteretic model, BWBN, was modified

to represent the hysteretic behavior of a nailed joint. Based on test data, suitable

parameters for different joint configurations can be estimated using a Genetic Algorithm.

This model was embedded in ABAQUS/Standard (Version 6.5), as a user-defined

element, which accounted for the coupling property of the nail joint action. Detailed

shear walls were simulated and analyzed, and the results agreed well with the test data.

iv

With some modifications on the nailed wood joint model, a super shear wall model

was developed, which describes the behavior of a whole shear wall line. This super shear

wall model consists of two diagonal hysteretic springs, along with the frame members in

the wall, and can predict racking and overturning behavior of shear walls at the same time.

Using this model, a 3-D 2-story building model, which was developed to simulate the

building tested in the CUREE shake table test (Fischer et al. 2001), was analyzed in

ABAQUS/Standard. Comparison of the results validated the accuracy and efficiency of

this super shear wall model.

Using this super shear wall model, a parametric study was conducted to benchmark

current design methods. The parameters included floor or roof diaphragm aspect ratios,

open-front ratios, and possible inclusion of gypsum partition walls. The study shows that

the elastic torsional design method is not satisfactory for open-front light-frame structures,

and design method improvement comments were made accordingly.

v

TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ............................................................................................. iii

ABSTRACT........................................................................................................................iv

LIST OF TABLES .............................................................................................................xi

LISTOF FIGURES ..........................................................................................................xiv

NOTATION................................................................................................................. xxviii

1. INTRODUCTION...........................................................................................................1

1.1 General.....................................................................................................................1

1.2 Open Front Light Frame Structure...........................................................................2

1.3 Objectives ................................................................................................................2

1.4 Scope and Limitations..............................................................................................3

2. BACKGROUND AND LITERATURE REVIEW.......................................................5

2.1 Introduction..............................................................................................................5

2.2 Nailed Wood Joint ...................................................................................................5

2.3 Wood-Frame Shear Wall .........................................................................................7

2.3.1 General............................................................................................................7

2.3.2 Previous Research on Wood-Frame Shear Wall.............................................8

2.3.3 The Logic of this study .................................................................................17

2.4 Summary ................................................................................................................18

vi

3. DEVELOPMENT OF NAILED WOOD JOINT ELEMENT IN

ABAQUS/STANDARD.....................................................................................................19

3.1 General...................................................................................................................19

3.2 A General Nailed Wood Joint Hysteretic Model...................................................20

3.2.1 Introduction...................................................................................................20

3.2.2 Parameters.....................................................................................................22

3.2.3 Model Solving...............................................................................................33

3.2.4 Parameter Estimation ....................................................................................34

3.2.5 Coupling Character .......................................................................................39

3.2.6 Modeling in ABAQUS/Standard ..................................................................42

3.2.6.1 Introduction of ABAQUS/Standard...................................................42

3.2.6.2 Hysteretic Nailed Wood Joint Model in ABAQUS/Standard ............43

3.3 Summary ................................................................................................................44

4. DETAILED SHEAR WALL MODELING.................................................................45

4.1 General...................................................................................................................45

4.2 The 1219×2438 mm (4×8 ft) Shear Wall Model (without opening) .....................46

4.2.1 Introduction...................................................................................................46

4.2.2 Shear Wall with Full Anchorage ...................................................................53

4.2.3 Shear Wall with Intermediate Anchorage ....................................................57

4.3 12×8 ft Shear Wall Model (with an opening) .......................................................65

4.3.1 Introduction...................................................................................................65

4.3.2 Shear Wall with Full Anchorage ...................................................................69

vii

4.3.3 Shear Wall with Intermediate Anchorage .....................................................77

4.4 Summary ................................................................................................................79

5. SUPER FEM SHEAR WALL MODEL .....................................................................80

5.1 General...................................................................................................................80

5.2 Model Development...............................................................................................82

5.3 Model Validation ...................................................................................................84

5.4 Summary ................................................................................................................89

6. 3-D WOOD-FRAME STRUCTURE MODELING...................................................90

6.1 Brief Introduction of the CUREE-Caltech Woodframe Project ............................90

6.2 CUREE 2-Story Wood-Frame Structure Test at UCSD........................................91

6.3 Detailed Shear Wall Modeling...............................................................................92

6.3.1 Material Properties........................................................................................92

6.3.2 Nail Joint Modeling ......................................................................................93

6.3.3 Detailed Shear Wall Modeling......................................................................96

6.4 Super Shear Wall Model Parameter Estimation ..................................................107

6.5 3-D Dynamic Model ............................................................................................109

6.5.1 Assumptions................................................................................................109

6.5.2 Description of the 3-D Model .....................................................................109

6.6 Result Comparisons ............................................................................................. 112

6.7 Result Analysis and Conclusions......................................................................... 118

6.8 Discussion on the Influence from Shear Wall Out-of-plane Action.................... 119

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vii

7. OPEN-FRONT WOOD-FRAME STRUCTURE PARAMETRIC STUDY..........120

7.1 Introduction..........................................................................................................120

7.2 Model Configurations ..........................................................................................121

7.3 Structural Modeling Techniques..........................................................................122

7.3.1 Floor Diaphragm Model .............................................................................122

7.3.2 Shear Wall Model........................................................................................122

7.3.3 Simulation of Gypsum Wall .......................................................................127

7.4 Structural Design .................................................................................................128

7.5 Analysis Results...................................................................................................133

7.6 Summary ..............................................................................................................189

7.7 Structural Response under Two-directional Ground Motion...............................196

7.7.1 Introduction.................................................................................................196

7.7.2 Two-directional Time History Analysis ......................................................196

7.7.3 Summary .....................................................................................................201

8. SUMMARY, CONCLUSIONS, AND FUTURE RESEARCH ...............................203

8.1 Summary ..............................................................................................................203

8.2 Conclusions..........................................................................................................204

8.3 Future Research ...................................................................................................208

REFERENCE..................................................................................................................210

APPENDIX A. CORRELATION COEFFICIENT.....................................................218

ix

APPENDIX B. SHEAR WALL DESIGN FOR THE PARAMETRIC STUDY.......220

APPENDIX C. RESULTS OF THE PARAMETRIC STUDY...................................225

x

LIST OF TABLES

4.1 Structural details of wall specimens tested by Salenikovich (2000) ......................47

4.2 Anchorage conditions for model and tested by Salenikovich (2000) .....................49

4.3 Mechanical Properties of OSB Panels (Courtesy of Salenikovich (2000)) ............50

4.4 End-grain-withdraw Performance Statistics............................................................61

4.5 Structural details of wall specimens..........................................................................69

4.6 Sheathing materials and nailing schedule (courtesy to Toothman (2003)) ...........74

5.1 Quantification of Model Accuracy ...........................................................................89

6.1 Properties of Frames and Diaphragms...................................................................111

6.2 Comparison of Ultimate Drifts and Reactions .......................................................118

7.1 Front Wall Design (L:W = 1:1) ...............................................................................131

7.2 Back Wall Design (L:W = 1:1) ................................................................................131

7.3 Perpendicular Wall Design (L:W = 1:1) ................................................................131

7.4 Torsion Design Results .............................................................................................133

7.5 Peak Drifts of the Shear Walls (Group 1_1)...........................................................143

7.6 Peak Imposed Loads and Load Ratios in the Shear Walls (Group 1_1) .............143

7.7 Peak Drifts of the Shear Walls (Group 1_2)...........................................................154

7.8 Peak Imposed Loads and Load Ratios in the Shear Walls (Group 1_2) .............154

7.9 Summary of the Design Recommendations............................................................195

7.10 Single-directional & Two-directional Earthquake Time History Analysis

Results ......................................................................................................................198

7.11 Perpendicular Shear Wall Parameter Update .....................................................201

7.12 Updated Two-directional Earthquake Time History Analysis Results ..............201

xi

B.1 Front Wall Design (Group 2_1) .............................................................................220

B.2 Back Wall Design (Group 2_1) ..............................................................................220

B.3 Perpendicular Wall Design (Group 2_1) ...............................................................220







B.10 Front Wall Design (Group 5_1) ...........................................................................223

B.11 Back Wall Design (Group 5_1) ............................................................................224

B.12 Perpendicular Wall Design (Group 5_1) .............................................................224

C.1 Peak Drifts of the Shear Walls (Group 2_1) .........................................................228

C.2 Peak Imposed Loads and Load Ratios in the Shear Walls (Group 2_1) ...........229








C.10 Peak Imposed Loads and Load Ratios in the Shear Walls (Group 4_1) .........248

C.11 Peak Drifts of the Shear Walls (Group 4_2) .......................................................252

xii






xiii

LIST OF FIGURES

3.1 Schematic Model .........................................................................................................21

3.2 Effect of a....................................................................................................................23

3.3 Effect of b and g on the Shape of the Hysteretic Curve.........................................24

3.4 Effect of n on the Shape of the Hysteretic Curve.....................................................25

3.5 Effect of dh on the Shape of the Hysteresis ..............................................................26

3.6 Effect of dn on the Shape of the Hysteresis ..............................................................27

3.7 Pinching Lag Phenomena...........................................................................................29

3.8 Elimination of Pinching Lag Phenomena .................................................................30

3.9 Realization of Small Loops.........................................................................................33

3.10 Validations of the Nailed Wood Joint Model .........................................................39

3.11 Oriented Spring Pair Model ....................................................................................40

4.1 Typical Wall assembly (Courtesy of Heine (1997)) .................................................48

4.2 Testing Plan (Courtesy of Heine(1997)) ...................................................................48

4.3 4×8 ft Shear Wall Specimens (Courtesy of Salenikovich (2000)) ..........................50

4.4 Meshing of Detail Model in ABAQUS ......................................................................51

4.5 Sheathing-framing Nail Connector Parameter Estimation ....................................52

4.6 International Standards Organization (ISO) loading protocol ..............................52

4.7 4×8 ft Shear Wall Hysteretic Loops from Testing (w/ tie downs) ..........................54

4.8 4×8 ft Shear Wall Hysteretic Loops from Model Analysis (w tie downs) .............54

4.9 Comparison of 4×8 ft Shear Wall Hysteretic Loops (w/ tie downs) ......................55

4.10 Comparison of 4×8 ft Shear Wall Hysteretic Energy (w/ tie downs) ..................55

xiv

4.11 4×8 ft Shear Wall Deformed Shape (w/ tie downs) ...............................................56

4.12 4×8 ft Shear Wall Sheathing Panel Misses Stress Contour (w/ tie downs) .........57

4.13 4×8 ft Shear Wall Hysteretic Loops from Testing (w/o tie downs) ......................58

4.14 4×8 ft Shear Wall Hysteretic Loops from Model Analysis (w/o tie downs) ........58

4.15 Comparison of 4×8 ft Shear Wall Hysteretic Loops (w/o tie downs) ..................59

4.16 End-grain-withdraw Load-Displacement Curves..................................................60

4.17 Pictures of the 4×8 ft Shear Walls with Intermediate Anchorage tested by

Salenikovich (2000) .................................................................................................62

4.18 4×8 ft Shear Wall Deformed Shape (w/o tie downs) .............................................64

4.19 4×8 ft Shear Wall Sheathing Panel Misses Stress Contour (w/o tie downs) .......64

4.20 12×8 ft Shear Wall Fabrication................................................................................66

4.21 12×8 ft Shear Wall Element Layout ........................................................................67

4.22 Gypsum Boards Installation in 12×8 ft Shear Wall ...............................................68

4.23 Sequential Phased Displacement (SPD) Protocol...................................................70

4.24 12×8 ft Shear Wall Hysteretic Loops from Testing (w/ tie downs) ......................71

4.25 12×8 ft Shear Wall Hysteretic Loops from Model Analysis (w/ tie downs) ........71

4.26 Comparison of 12×8 ft Shear Wall Hysteretic Loops (w/ tie downs) ..................72

4.27 12×8 ft Shear Wall Deformed Shape (w/ tie downs) .............................................72

4.28 12×8 ft Shear Wall Sheathing Panel Misses Stress Contour (w/ tie downs) .......73

4.29 Tested 4×8 ft Shear Wall Hysteretic Loops (w/ tie downs) ..................................75

4.30 Tested 4×8 ft Shear Wall Load Envelops (w/ tie downs) ......................................75

xv

4.31 12×8 ft Shear Wall Load Envelops (w/ tie downs) ................................................76

4.32 Load Ratio Comparison (w/ tie downs) .................................................................76

4.33 Comparison of 12×8 ft Shear Wall Hysteretic Loops (w/o tie downs) ................77

4.34 12×8 ft Shear Wall Deformed Shape (w/o tie downs) ...........................................78

4.35 12×8 ft Shear Wall Sheathing Panel Misses Stress Contour (w/o tie downs) .....78

5.1 Single-spring Super Shear Wall Model.....................................................................80

5.2 Diagonal-spring Super Shear Wall Model................................................................81

5.3 Super Shear Wall Model Considering Overturning Effect.....................................82

5.4 Racking of Diagonal-Spring Shear Wall Model.......................................................84

5.5 4×8 ft Solid Shear Wall Validation (according to test data w/ hold downs) .........85

5.6 12×8 ft Open Shear Wall Validation (according to test data w/ hold downs) ......86

5.7 4×8 ft Solid Shear Wall Validation (according to detailed wall model analysis

results w/ hold downs) ............................................................................................87

5.8 12×8 ft Open Shear Wall Validation (according to detailed wall model analysis

results w/ hold downs) ............................................................................................88

6.1 Flowchart of the Organization of the Various Tasks ..............................................91

6.2 Elevations of Phase-9 Test Structure Showing Major Structural Components

(Fischer, et al 2001) .................................................................................................93

6.3 Parameter Estimation of the Single Nail Joint.........................................................94

6.4 Nail Joint Cyclic Test Results from Fischer, et al (2001) (Perpendicular to Grain)

…………………………………………………………………………………………….95

6.5 Nailed Joint Cyclic Test Results from Fischer, et al (2001) (Parallel to Grain) ...96

xvi

6.6 1st-story East Wall Configuration and Detailed Model ..........................................98

6.7 1st-story West Wall Configuration and Detailed Model .........................................99

6.8 2nd-story East and West Wall Configuration and Detailed Model .....................100

6.9 1st and 2nd Story North & South Wall Detailed Model........................................102

6.10 1st-story East Wall Analysis Results .....................................................................103

6.11 1st-story West Wall Analysis Results....................................................................104

6.12 2nd-story East and West Wall Analysis Results ..................................................105

6.13 1st and 2nd-story South and North Wall Analysis Results ................................106

6.14 Super Shear Wall Parameter Estimation of 1st-story East Wall ......................107

6.15 Super Shear Wall Parameter Estimation of 1st-story West Wall .....................107

6.16 Super Shear Wall Parameter Estimation of 2nd-story East and West Wall.....108

6.17 Super Shear Wall Parameter Estimation of 1st and 2nd-story North and South

Wall ......................................................................................................................108

6.18 Input Ground Acceleration History ......................................................................112

6.19 Comparison of Experimental and Numerical Mode Shapes...............................113

6.20 1st-story East Wall Relative Displacement History for Level-4 Earthquake

Input (Correlation Coefficient = 0.804) ..............................................................114

6.21 1st-story East Wall Relative Displacement History for Level-5 Earthquake

Input (Correlation Coefficient = 0.804) ..............................................................114

6.22 Global Relative Displacement History for Level-4 Earthquake Input

(Correlation Coefficient = 0.829) .........................................................................115

6.23 Global Relative Displacement History for Level-5 Earthquake Input

(Correlation Coefficient = 0.929) .........................................................................115

xvii

6.24 Global Hysteresis Comparison for Level-4 Earthquake Input...........................116

6.25 Global Hysteresis Comparison for Level-5 Earthquake Input...........................117

7.1 Ground Motion History (peak acceleration = 0.5 g) .............................................121

7.2 Plan Views of The Buildings ....................................................................................123

7.3 4×8 ft Gypsum Wall Parameter Estimation ...........................................................127

7.4 Gypsum Wall Hysteretic Energy Comparison.......................................................128

7.5 Response Spectra Comparison ................................................................................129

7.6 Drifts of Perpendicular Walls (Case 1_1_0) ...........................................................134

7.7 Drifts of Perpendicular Walls (Redesigned Case 1_1_0).......................................134

7.8 Drifts of Parallel Walls (Case 1_1_0) .....................................................................134

7.9 Drifts of Parallel Walls (Redesigned Case 1_1_0) .................................................135

7.10 Drifts of Perpendicular Walls (Case 1_1_25) ......................................................135

7.11 Drifts of Perpendicular Walls (Redesigned Case 1_1_25)...................................135

7.12 Drifts of Parallel Walls (Case 1_1_25) ..................................................................136

7.13 Drifts of Parallel Walls (Redesigned Case 1_1_25)..............................................136

7.14 Drifts of Perpendicular Walls (Case 1_1_50) .......................................................136


7.16 Drifts of Perpendicular Walls (Case 1_1_75) .......................................................137


7.18 Drifts of Perpendicular Walls (Case 1_1_100) .....................................................138

7.19 Drifts of Parallel Walls (Case 1_1_100) ................................................................138

7.20 Peak Perpendicular Wall Drift (L:W=1:1, w/o partition wall) .........................139

7.21 Peak Parallel Wall Drift (L:W=1:1, w/o partition wall) .....................................140

i

xvii

7.22 Peak Perpendicular Impose Load (L:W=1:1, w/o partition wall) .....................141

7.23 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:1, w/o partition

wall) ......................................................................................................................141

7.24 Peak Parallel Impose Load (L:W=1:1, w/o partition wall) ................................142

7.25 Peak Parallel Imposed Load / Design Resistance (L:W=1:1, w/o partition wall)

......................................................................................................................143

7.26 Drifts of Perpendicular Walls (Case 1_2_0) ........................................................144

7.27 Drifts of Parallel Walls (Case 1_2_0) ...................................................................145

7.28 Drifts of Partition Wall (Case 1_2_0) ...................................................................145


7.30 Drifts of Parallel Walls (Case 1_2_25) .................................................................146

7.31 Drifts of Partition Wall (Case 1_2_25) .................................................................146







7.38 Drifts of Perpendicular Walls (Case 1_2_100) ....................................................148

7.39 Drifts of Parallel Walls (Case 1_2_100) ...............................................................149

7.40 Drifts of Partition Wall (Case 1_2_100) ...............................................................149

7.41 Back Wall Hysteresis .............................................................................................150

7.42 Partition Wall Hysteresis .......................................................................................150

xix

7.43 Peak Perpendicular Wall Drift (L:W=1:1, w/ partition wall) ...........................151

7.44 Peak Parallel Wall Drift (L:W=1:1, w/ partition wall) .......................................152

7.45 Peak Perpendicular Impose Load (L:W=1:1, w/ partition wall) .......................152

7.46 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:1, w/ partition

wall) ......................................................................................................................153

7.47 Peak Parallel Impose Load (L:W=1:1, w/ partition wall) ..................................153

7.48 Peak Parallel Imposed Load / Design Resistance (L:W=1:1, w/ partition wall)

......................................................................................................................154

7.49 Peak Parallel Base Shear (L:W=1:1) ...................................................................155

7.50 Peak Perpendicular Wall Drift (L:W=1:2, w/o parallel partition wall) ...........156

7.51 Peak Parallel Wall Drift (L:W=1:2, w/o parallel partition wall) ......................157

7.52 Peak Perpendicular Imposed Load (L:W=1:2, w/o parallel partition wall) ....158

7.53 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:2, w/o parallel

partition wall) ........................................................................................................158

7.54 Peak Parallel Imposed Load (L:W=1:2, w/o parallel partition wall) ................159

7.55 Peak Parallel Imposed Load / Design Resistance (L:W=1:2, w/o parallel

partition wall) ........................................................................................................160

7.56 Peak Perpendicular Wall Drift (L:W=1:2, w/ parallel partition wall) .............161

7.57 Peak Parallel Wall Drift (L:W=1:2, w/ parallel partition wall) ........................161

7.58 Peak Perpendicular Imposed Load (L:W=1:2, w/ parallel partition wall) ......162

7.59 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:2, w/ parallel

partition wall) ........................................................................................................162

7.60 Peak Parallel Imposed Load (L:W=1:2, w/ parallel partition wall) ..................163

xx

7.61 Peak Parallel Imposed Load / Design Resistance (L:W=1:2, w/ parallel

partition wall) ........................................................................................................163


7.63 Peak Perpendicular wall Drift (L:W=1:3, w/o parallel partition wall) ............165

7.64 Peak Parallel wall Drift (L:W=1:3, w/o parallel partition wall) ........................165

7.65 Peak Perpendicular Imposed Load (L:W=1:3, w/o parallel partition wall) ....166

7.66 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:3, w/o parallel

partition wall) ........................................................................................................166

7.67 Peak Parallel Imposed Load (L:W=1:3, w/o parallel partition wall) ................167

7.68 Peak Parallel Imposed Load / Design Resistance (L:W=1:3, w/o parallel

partition wall) ........................................................................................................167

7.69 Peak Perpendicular Wall Drift (L:W=1:3, w/ parallel partition wall) .............168

7.70 Peak Parallel Wall Drift (L:W=1:3, w/ parallel partition wall) ........................169

7.71 Peak Perpendicular Imposed Load (L:W=1:3, w/ parallel partition wall) ......169

7.72 Peak Perpendicular Imposed Load / Design Resistance (L:W=1:3, w/ parallel

partition wall) ........................................................................................................170

7.73 Peak Parallel Imposed Load (L:W=1:3, w/ parallel partition wall) ..................170

7.74 Peak Parallel Imposed Load / Design Resistance (L:W=1:3, w/ parallel

partition wall) ........................................................................................................171




7.78 Peak Perpendicular Imposed Load (L:W=2:1, w/o partition wall) ...................173

xxi


wall) ......................................................................................................................174

7.80 Peak Parallel Imposed Load (L:W=2:1, w/o partition wall) ..............................175


......................................................................................................................175



7.84 Peak Perpendicular Imposed Load (L:W=2:1, w/ partition wall) .....................177


wall) ......................................................................................................................178

7.86 Peak Parallel Imposed Load (L:W=2:1, w/ partition wall) ................................178


......................................................................................................................179




7.91 Peak Perpendicular Imposed Load (L:W=3:1, w/o partition wall) ...................182


wall) ......................................................................................................................183

7.93 Peak Parallel Imposed Load (L:W=3:1, w/o partition wall) ..............................183


......................................................................................................................184


xxii


7.97 Peak Perpendicular Imposed Load (L:W=3:1, w/ partition wall) .....................186


wall) ......................................................................................................................186

7.99 Peak Parallel Imposed Load (L:W=3:1, w/ partition wall) ................................187


......................................................................................................................187

7.101 Peak Parallel Base Shear (L:W=3:1) .................................................................188

7.102 Open-front Building under Transverse Loading ..............................................194

7.103 Ground Motion History in Minor Direction (peak acceleration = 0.43 g) ......197

7.104 Plan Views of Buildings 1_1_50, 2_1_0, and 3_1_0............................................198

C.1 Drifts of Perpendicular Walls (Case 2_1_0) ..........................................................225

C.2 Drifts of Parallel Walls (Case 2_1_0) .....................................................................225

C.3 Drifts of Perpendicular Walls (Case 2_1_25) ........................................................226

C.4 Drifts of Parallel Walls (Case 2_1_25) ...................................................................226





C.9 Drifts of Perpendicular Walls (Case 2_1_100) ......................................................228

C.10 Drifts of Parallel Walls (Case 2_1_100) ...............................................................228



xxiii


C.14 Drifts of Parallel Walls (Case 2_2_25) .................................................................230





C.19 Drifts of Perpendicular Walls (Case 2_2_100) ....................................................232

















xxiv








C.43 Drifts of Perpendicular Walls (Redesigned Case 4_1_0)....................................242

C.44 Drifts of Parallel Walls (Redesigned Case 4_1_0)...............................................242



C.47 Drifts of Perpendicular Walls (Redesigned Case 4_1_25)..................................243

C.48 Drifts of Parallel Walls (Redesigned Case 4_1_25).............................................243











xxv













C.71 Drifts of Perpendicular Walls (Redesigned Case 5_1_0)....................................253

C.72 Drifts of Parallel Walls (Redesigned Case 5_1_0)...............................................253










xxvi
















xxvii

NOTATION

BWBN = a hysteretic model named after the four developers’ last name initials;

c = linear viscous damping coefficient;

er = eccentricity between mass center and stiffness center;

F = nail joint force vector in the global coordinate;

F’ = nail joint force vector in the local coordinate of Oriented Spring Pair

Model;

F(t) = time-dependant forcing function;

Fu = nail joint force along the moving trajectory;

Fv = nail joint force perpendicular to the moving trajectory;

f(t) = mass-normalized forcing function;

g = acceleration of gravity (32.2 ft/s2 or 9.8 m/s2);

H = restoring force in the hysteretic spring;

h(z) = pinching function;

[K] = nail joint stiffness matrix in the global coordinate;

[K’] = nail joint stiffness matrix in the local coordinate of Oriented Spring Pair

Model;

K0 = initial lateral stiffness of structure;

K11, K12, K22= terms in the nail joint stiffness matrix in the global coordinate;

Ku = tangent stiffness of the nonlinear spring along the moving trajectory;

Kv = tangent stiffness of the nonlinear spring perpendicular to the moving

trajectory;

kt = total tangent stiffness of the elastic and hysteretic springs;

i

xxvii

L = building dimension in the direction perpendicular to ground motion;

m = mass;

M_Dis = the maximum positive displacement (when u>0) or absolute value of the

minimum displacement (when u≤0)

Max_Dis= the maximum positive displacement;

Min_Dis= the minimum displacement;

n = hysteresis shape parameters (controls curve smoothness)

p = rate of change of 1ζ ;

q = fraction of ultimate hysteretic strength, zu, where pinching occurs;

R = total restoring force from both the linear and hysteretic springs;

r = mass-normalized restoring force;

ratio = ratio of the displacement at unloading position to the experienced

maximum displacement in the same direction;

S = restoring force in the linear spring;

sgn(.) = the signum function;

[T] = stiffness transform matrix

T = torsion moment;

u = relative displacement of the mass to the base;

u& = relative velocity of the mass to the base;

u&& = relative acceleration of the mass to the base;

V// = total parallel design resistance;

V⊥ = imposed load in perpendicular walls;

W = building dimension in the direction parallel to ground motion;

xxix

z = hysteretic displacement;

zu = ultimate hysteretic displacement;

α = rigidity ratio;

β = hysteresis shape parameters

γ = hysteresis shape parameters

ηδ = stiffness degradation rate;

νδ = strength degradation rate;

ψδ = rate of change of 2ζ ;

ε = hysteretic energy dissipation;

1ζ = pinching parameter controls the pinching stiffness (0.0< 1ζ

ω1 = circular frequency of the structural fundamental vibration mode;

ωxi = value of parameter, ω of the ith shear wall parallel to the ground motion

direction;

ωyi = value of parameter, ω of the ith shear wall perpendicular to the ground

motion direction;

xxxi

To My Parents, Jiuying Liu & Xiangming Xu

To My Wife, Xiaohui Huang

xxxii

Chapter 1 Introduction

1.1 General

In the past few decades, many severe earthquakes were recorded all around the world.

The Northridge earthquake (USA, 1994) statistics include 56 dead, 25,000 dwellings

uninhabitable, and $10 billion in damage. In the Chichi earthquake (Taiwan, 1999), the

death toll surpassed 2,400 and more than 10,700 people were injured. Over 8,500

buildings were destroyed and another 6,200 were seriously damaged, a majority of which

were reinforced concrete structures with poorly designed columns that failed at the first

story. The Turkey (1999) and Pakistan earthquakes (2005) killed more than 80,000 people.

The significant losses caused by these earthquakes have raised the public’s concern about

improving the engineering and reliability of structures.

Recently, research in the area of structural disaster resistance has changed from static

to dynamic, from monotonic loading to reversed cyclic loading, and from element level

to system level. These changes are due to the fact that the structural behavior under

natural disasters is more dynamic based, and the structures behaved more as a whole

system than as several separate parts. Connections between members and the structural

configurations govern the structural behavior much more than the response of single

members. Without a theoretical understanding of the real dynamic performance of the

structure in ultimate situations, designs can be unsafe and even ridiculous.

Low-rise residential houses and small commercial buildings in North America are

generally light-frame structures constructed using steel and/or wood-based materials.

1

Typically, frames are used to resist the vertical loading, and the roof, floors, and shear

walls form the lateral force resisting system. The high strength-to-weight ratio of

wood-based materials, the ductility of connectors, and the high redundancy of the system

are three main reasons that light-frame structures perform well when subjected to seismic

events.

1.2 Open Front Light-frame Structure

Post event damage reports show irregular structural configurations are likely

contributors to the failure of a large number of buildings during earthquakes. Open front

construction is a common plan irregular case.

Because of plan irregularity, open-front light-frame structures will suffer from

torsion problems when subjected to major seismic events if not designed properly. The

methodology used in the current codes for the structures with torsional irregularity is in

the elastic domain, and the design requirements are not detailed enough. On the other

hand, design in areas with significant seismic risk relies on inelastic response, which

means that the assumptions of the elastic analysis are not valid. The displacement mode

and distribution of lateral loads in shear walls of open front structures can be very

different from those determined using elastic analysis. Besides, the displacement ductility

demand on certain elements may be significantly larger than the demand imposed on the

system as a whole. The elastic design methods can be unsafe and sometimes misleading.

1.3 Objectives

Full-size testing is a good tool to show the real performance of open-front

2

light-frame structure systems under significant lateral loadings. However, it is not

possible to test structures of all configurations. To better understand the behavior of

open-front light-frame structures under significant lateral loadings, a numerical model,

which can accurately predict the dynamic hysteretic performance of light-frame

structures under lateral dynamic loads, is needed. Unfortunately, commercially available

software does not have the appropriate elements which are able to accurately describe the

hysteretic behavior of light-frame systems. The accuracy and versatility of the models

developed and used in most available research tools are not satisfactory. So developing a

more accurate and reliable model is one of the objectives of this study.

Using this developed model as a tool, a parametric study was completed to quantify

the responses of open-front light-frame buildings under significant lateral loadings (the

parameters include the open-front ratio or irregular degree, building aspect ratio, and the

presence of nonstructural partition walls or not). Time history analysis was conducted on

a series of models with different configurations. The curves describing structural

behavior based on the parametric study are used as a reference to real design practice, and

some design recommendations are made at the end.

1.4 Scope and Limitations

Although the model developed in this study is a general one that can be employed to

represent many different kinds of structures with some parameter modifications, this

study focuses on low-rise wood light-frame structures.

In this study, only the short-duration behavior is considered. Effects attributed to

‘time effects’ such as moisture content variations, as well as creep, weathering, or aging,

3

are not considered.

The procedure of the research includes the following steps.

1. Modify BWBN (a mathematical model which used a series of differential

equations to describe the hysteretic rules) to make it suitable for nailed wood

joints and light-frame shear walls.

2. Employ an optimization method to estimate the parameters associated with

relevant joint configurations.

3. Embed the nailed wood joint model into ABAQUS/Standard and simulate

detailed shear wall models in ABAQUS.

4. Develop a super shear wall model (consists of frame members and a pair of

diagonal hysteresis springs), which can also take overturning into account.

5. Simulate the 2-story full-scale building tested in UC, San Diego for CUREE

with the super shear wall model and validate the proposed super shear wall

model through the comparison of the experimental and simulation results.

6. Build a series of models with different aspect ratios and open-front ratios, and

run nonlinear time history analysis. Then complete a parametric study on the

torsional behavior of open-front light-frame structures subjected to lateral

forces (the possible parameters include the open-front ratio or irregularity

degree, building length-width ratio, and diaphragm rigidity, etc.).

7. Develop curves and tables based on the parametric study results, which can be

used as a reference in real design practice.

4

Chapter 2 Background and Literature Review

2.1 Introduction

In a wood-frame structural system, shear wall is the most important lateral-resistant

element. The ductility of a wood-frame shear wall is from the hysteretic behavior of

nailed wood joints between sheathing panels and framing members. Many studies have

been conducted on numerical simulation of the hysteretic behavior of nailed wood joints

and shear walls. Some important researches were briefly introduced in this chapter.

2.2 Nailed Wood Joint

Hysteretic performance of nailed wood joints is quite complicated. It primarily

depends on the nail material and manufacture, and the embedment property of the wood.

Friction between nail and wood, and between wood members also affects the joint

performance to some extent.

For decades, many researchers have conducted work to find a way to accurately

describe the mechanical behavior of a nail joint. Based on the Takeda model, which was

developed to model the hysteretic rule of reinforced concrete members under reversed

lateral loading (briefly described in Loh et al 1990), Kivell et al. (1981) derived a

hysteresis model suitable for moment resisting nailed timber joints. This model uses a

pair of symmetric bi-linear paths as the backbone curve. The track between the maximum

deflection on the positive backbone curve and that on the negative part is described with

a tri-linear path. The end points of the three lines are defined by a cubic function that

5

passes through the maximum deflections. This model was used to analyze the dynamic

performance of two simple timber portal frames with nailed beam-to-column connections.

Pinching could be represented in this model, however, the system degradation was not

considered.

Polensek and Laursen (1984) developed a hysteresis model for nailed

plywood-to-wood connections based on test data. The model is similar to that of Kivell et

al. (1981). The difference is that a tri-linear curve is used as the backbone curve and the

governing points on the tri-linear trace between positive maximum deflection and

negative maximum deflection are obtained using a statistical fit of test data.

Instead of multiple-linear curves, Dolan (1989) derived a hysteresis model described

by an exponential backbone curve and four unloading and reloading sections, which are

defined by different exponential equations. The backbone curve equation was first

developed by Foschi (1977). Dolan modified it to take strength degradation into account.

The parameters used in this model are based on a statistical fit of test data.

Ceccotti and Vignoli (1990) developed a hysteresis model for moment-resisting

semi-rigid wood joints that are normally used in glulam portal frames in Europe. The

pinching and stiffness degradation are considered in this model, and the element was

incorporated into the commercial non-linear dynamic analysis program DRAIN-2D.

Chui et al (1997, 1998) developed a finite-element model for nailed wood joints

under cyclic load. Three types of elements are used in this model: a beam element to

represent the nail, a spring element for embedment, and a linkage element for friction

between nail and wood. The method developed by Dolan (1989) was employed to

describe the embedment spring element.

6

Foschi (2000) represented the nail with a beam element and the embedment action

between nail and wood with a nonlinear spring element. The embedment property is

determined from test data. The gap between nail and wood is considered explicitly (i.e.,

the force will not be built in the spring between nail and wood until the deflection of the

nail is beyond the gap size). This model ignored the friction between fastener and wood,

and the withdrawal effect of the fastener, which are important for the nail joint

performance under cyclic loading. He et al. (2001) modified and used this model in the

modeling of three-dimensional timber light-frame buildings.

All these hysteresis models for nailed wood joints were derived from specific joint or

system configurations and were expressed with either a complex set of force-history rules

or limited empirical relations. To overcome these disadvantages, a general hysteresis

model, which can simulate a wide variety of nailed wood joints, is needed.

2.3 Wood-frame Shear Wall

2.3.1 General

Wood-frame Shear Walls are mainly designed to resist in-plane lateral loads caused

by wind or earthquakes. A typical wood-frame shear wall is built using wood framing

members (studs, sill plates, and top plates) and sheathing panels (plywood or OSB panels,

etc). The wood framing members form a stand on which the sheathing panels are attached

by nails or other types of discrete fasteners. The framing members are used to resist

vertical loads and the out-of-plane loading (e.g. the wind flowing perpendicular the wall

face). The in plane lateral loads are resisted by the racking of the sheathing panels. Tests

have shown that the most common failure mode of a shear wall under lateral loads is the

7

tearing and pullout of the sheathing fasteners. On the other hand, the sheathing fasteners

are also the source of the ductility of the shear wall. Basically, the performance of the

sheathing fasteners controls the shear wall behavior.

Since shear walls are the most important component within the light-frame building

system, modeling of shear walls is the most important part in modeling of the whole

system. To simulate shear walls accurately and efficiently through the finite element

method (FEM) is one of the main objectives of this study.

2.3.2 Previous Research on Wood-Frame Shear Walls

To understand the characteristics of shear wall performance better, large numbers of

studies, including testing and modeling, have been completed. Some of the more recent

studies will be described here.

Heine (1997) tested sixteen full-scale wall specimens using monotonic and

sequential phased displacement (SPD) patterns. A total of five different wall

configurations, five anchorage, and two loading conditions were used. All walls were 2.4

m (8 ft) high. Straight wall specimens were 12.2 m (40 feet) long, whereas specimens

with return corner walls measured 3.7 m (12 ft) in length. He investigated the monotonic

and cyclic response of light-frame wood shear walls with and without openings. The test

results show that the amount of overturning restraint is positively correlated with ultimate

capacity and elastic stiffness. The influence magnitude is related to the opening ratio of

the shear walls (i.e., the bigger the opening, the more the stiffness and capacity

improvement is affected). Furthermore, effects of overturning restraint in the form of

tie-down anchors and corner segments on light-frame shear walls with and without door

8

and window openings were quantified. He also found that, without overturning restraints,

shear walls exhibit a pronounced rigid-body rotation arising from uplift and separation

along the bottom plate. The main failure mode was sheathing and stud separation from

the bottom plate.

Salenikovich (2000) studied the response of light-frame timber shear walls to lateral

forces. He obtained performance characteristics of shear walls with various aspect ratios

and overturning restraint via experimental testing and analytical modeling. Fifty-six

light-frame timber shear walls with aspect ratios of 4:1, 2:1, 1:1, and 2:3 were tested.

Overturning restraint conditions of engineered construction (walls were attached to the

base through tie-down anchors and shear bolts) and conventional construction practices

(walls were attached to the base through nails or shear bolts only) were investigated. To

remove the influence of self-weight, the specimens were tested in a horizontal position

with OSB sheathing on one side. The nail-edge distance across the top and bottom plates

varied from 10 mm (3/8 in.) to 19 mm (3/4 in.). A mechanics-based model was advanced

to predict the racking resistance of conventional multi-panel shear walls using simple

formulae. The deflections of engineered and conventional shear walls were predicted

using the energy method combined with empirical formulae to account for load

deformation characteristics of sheathing-to-framing connections and overturning

restraint.

The study prepared by McKee, et al. (1998) focused on the performance of

perforated shear walls with narrow wall segments. The objective of this study was to

understand the influence of the width of the full-height segments, the reduced base

restraint and alternative framing methods on the performance of light-frame shear walls.

9

In this study, 7 light-frame shear wall specimens were tested. The first specimen was a

fully sheathed one and was tied down at both ends with two hold-down anchors, which

was used as a control. The rest of the walls were constructed with different opening ratios,

different opening configurations, different base restraints, and different framing methods.

The test results validated a conservative capacity estimation for perforated shear wall

method (Sugiyama and Matsumoto, 1994). An alternative prediction equation for shear

load ratio was presented and was proved to be more accurate than the former one. The

test data showed that a significant portion of the load was shared with the rest of the

full-height wall segments because of the shear transfer through the sheathing above and

below the openings. The tests showed that the initial stiffness was proportional to the

sheathing area ratio. The truss plate reinforcement placed at wall corners and opening

corners increased the initial stiffness, the ultimate capacity, and the energy dissipation

capacity of the wall significantly. The strap wrapped over the header and top plate

increased the ultimate capacity and the energy dissipation, and reduced the end stud’s

uplift significantly. The wall with wider segments (1219 mm, 4 ft) had a slightly greater

ultimate capacity and initial stiffness than did that with narrower segments (610mm, 2 ft)

(They had same opening ratio). However, the energy dissipation capacity of the former is

much lower that the later. Results also show that the increased anchor bolt spacing had

little effect on the specimen’s stiffness and energy dissipation. All walls tested had similar

failure characteristics. The initial loading was highly linear until the screws began to pull

through the GWB. Racking of full height OSB panels was observed, while the OSB

above and below openings acted as a rigid body. As failure progressed the nails failed

along the bottom plate in the walls with openings. This failure was more prevalent in the

10

wall section that had no hold-down anchor to resist overturning on the tension (uplift)

side of the wall specimen.

Kochkin, et al. (2001) conducted another testing study, which focused on the

performance of wood shear walls with corners. In this research, the researchers did some

monotonic-loading tests on 11 wood shear wall specimens (20ft X 8ft), one of which was

engineered (including hold-downs at both ends), and the others are perforated or

non-perforated (fully sheathed) conventional ones (no hold-downs) with 2-foot or 4-foot

corner return walls. The objectives of this research included: 1. Measuring the

performance of conventional wood shear walls (no hold-downs) and comparing results

with the data for engineered wood shear walls (including hold-downs). 2. Investigate the

restraining effect of the return corner on the lateral response of conventional wood shear

walls. 3. Examining the applicability of innovative design methods to conventional wood

shear walls restrained against overturning by corner framing.

The conclusions drawn from this research included: The corner-restrained

conventional walls have equivalent elastic stiffness as the engineered walls. Separation of

the sheathing panel from the bottom plate near the corner and bending failure of the

bottom plate were the typical failure modes for the bolted walls. Withdrawal of the

bottom plate nails from the platform was the typical failure mode for the nailed walls.

The failure of each wall was accompanied with an uplift failure of the return corner. The

corners provided the uplift resistance through the nails along the bottom plate. The

remaining sheathing nails of the corner panel showed little degradation. The walls with

4-foot corners approached or exceeded capacity of an engineered shear wall. However,

the ductility of the conventional walls decreased compared with engineered ones because

11

of the change of failure modes. The fully sheathed walls with the 4-foot corners reached

higher capacities and showed larger ductility characteristics than the fully sheathed walls

with the 2-foot corners. The perforated walls restrained with corners showed higher

ductility as compared to fully sheathed walls. The corner width had little influence on the

elastic stiffness. The Perforated Shear Wall (PSW) method considerably underestimated

capacity of the perforated shear walls restrained with corner returns but estimated the

stiffness well. The method proposed by Ni et al. (1998) provided more accurate results

and is more suitable for the analysis of conventional shear walls. The equation showed

that the ratio of the lateral load capacity of walls with partial uplift restraint to capacity of

wall with full uplift restraint is inversely proportional to the wall aspect ratio, which

means that the larger the wall aspect ratio is, the decrease in wall capacity caused by lack

of uplift restraint is greater. The effect of the door openings was not considered in this

study, which was thought to weaken the shear wall even more than windows do.

In accordance with the research of Ni and Karacabeyli (2000), a vertical load of 17.5

kN/m (1.2 kips/ft) on unrestrained walls was required to provide the same performance as

the wall with hold-downs. However, vertical load of 4.38 kN/m (0.3 kips/ft), which

counteracted 25% of the overturning moment, allowed the unrestrained wall to develop

80% of its full capacity and ultimate displacement (Validated for shear walls with aspect

ratio of 1).

Toothman (2003) did a series of 1219 × 2438 mm (4 × 8 ft) light-frame shear walls

with tie-downs and without tie-downs. The sheathing materials investigated included

OSB, hardboard, fiberboard, and gypsum wallboard. This study obtained and compared

performance characteristics of each sheathing material, and especially investigated the

12

contribution of gypsum in walls with dissimilar sheathing materials on opposite sides of

the wall. It also investigated the effects of monotonic loading versus the cyclic loading

response and the effects of using overturning anchors.

In addition to experimental studies, many researchers have made great efforts to

model the shear walls numerically. Tarabia and Itani (1997) accomplished modeling a

whole 3-D light-frame building using FEM. In this model, diaphragm elements are used

to represent walls. Master DOF’s were assigned to the connecting nodes among the

diaphragms. They also were assigned to the nodes with lumped masses for the dynamic

analysis. Three translational degrees-of-freedom were assigned to each master node. The

stiffness matrix of a diaphragm was divided into two parts, which were shear and bending

respectively (no coupling between these two actions). In this model, buckling of

sheathing panels was not considered, and 5 elements were used to represent the shear

wall. A 2-node linear element with two translational DOF at each end was used for the

frame. The DOF connected with master DOF through linear shape functions. For

sheathing, 2D plane elements were employed, which could deform in shear only with the

capacity to model openings within the sheathing panel. Sheathing interface elements were

used to prevent overlapping of adjacent sheathing panels. The stiffness values of these

springs were equal to zero in the case of separation, and higher values in the case of

contact. Linear springs with different values in tension, compression, and shear were used

for framing connectors. Sheathing-frame fasteners were modeled as a two-perpendicular

decoupled nonlinear spring system connecting sheathing and framing elements. A

lumping technique was used to evaluate the stiffness matrix of each group of nails located

on one line as a single element. The fastener stiffness was assumed to distribute along the

13

wall line and a numerical integration method was used to evaluate the total stiffness

matrix. Kivell et al.’s hysteretic model was used to represent the hysteretic performance

of nail connections and inter-component connections. Axial stiffness of inter-component

elements was based on the hysteresis rule developed in Tarabia (1994). The out-of-plane

bending deformations were assumed to be small and the behavior was assumed to be

linear. Rotational DOFs were condensed out using the static condensation process.

When considering out-of-plane bending action, the sheathing elements were modeled

with 4-node thin plate elements. Two rotational DOFs and one out-of-plane translational

DOF were assigned to each node. The bending stiffness matrix of the framing elements

was calculated first as a grid element with two rotational and one translational degrees of

freedom in the local coordinates axes and then transformed and condensed to retain the

master DOFs only. For out-of-plane action, the slippage between framing members and

sheathing panels was ignored.

Folz and Filiatrault (2001, 2004) formulated a FEM model to predict the hysteretic

performance of light-frame shear walls and formed the “pancake model” to simulate the

performance of a whole building. In this model, the connector and shear wall hysteresis

loops were composed of a backbone curve and some straight lines between maximum

displacement and minimum displacement. The parameters of nail connectors were

obtained from test data, and the shear wall spring’s parameters were based on the cyclic

analysis of shear walls which were composed of elastic shell elements, rigid frame

elements, and nonlinear nail connector elements between frames and shells. The straight

lines used in describing hysteresis loops could cause inaccuracy. Another problem is that

the same backbone is used for both monotonic and hysteresis curves. This usually is not

14

true for nail connector and shear wall performance. Actually, the monotonic capacity is

usually higher than the hysteretic capacity, especially when the number of loading cycles

is large, the capacity will degrade as the dissipated energy increases (Heine 1997,

Dinehart et al.1998).

This light-frame structure model simplified the 3D structural into a 2D planar model

composed of zero-height shear wall spring elements that connect the floor and roof

diaphragms together or to the foundation. All the horizontal diaphragms were assumed

in-plane rigid. This model has been incorporated into the computer program SAWS

(Seismic Analysis of Wood-frame Structures). The most obvious advantage of this model

is that it is very simple, and computer time is saved. The model predictions of both the

dynamic characteristics and seismic response of the structures are relatively accurate.

However, it cannot show the influence of the diaphragm rigidity on the torsional effect of

the structures. It cannot represent the influence of the roof slope effect, the out-of-plane

stiffness of the shear wall, or the interaction between intersecting shear walls, which are

generally perpendicular to each other. The most important thing is that it cannot capture

the overturning and flexural response of a structure. (Actually for low-rise light-frame

structures, the flexural response is not so apparent given enough hold-down capacity.)

Also, SAWS has limited functions compared with general commercial FEM software.

Collins, et al (2005) built a light-frame structure model in ANSYS, a commercial

FEM software. In this study, the nail connector model is based on a phenomenological

model presented by Dolan (1989) and Kasal and Xu (1997), which could exhibit the key

properties of the hysteretic response of these elements. In this shear wall model, a pair of

diagonal hysteretic nonlinear springs instead of one zero-height spring, which was

15

employed by Folz and Filiatrault (2004), was used to represent the in-plane action of

shear walls, and the hysteresis parameters for these springs were energetically equivalent

to experimental results or detailed FE models of individual walls, which are composed of

shells, beams, and nonlinear nail connection elements. Shell elements were used to

represent the sheathing, and beam elements were used to represent the framing. The shell

element used here has no membrane stiffness, so actually it is a plate element. Shell

elements and beam elements provide the out-of-plane resistance of the wall assembly. A

shell element layer accounts for the bending action of all the existing sheathing layers.

The moment of inertia is calculated using the parallel axis theorem. This simplification

does not account for slippage between the framing and sheathing. The axial resistance is

provided by the beam elements representing the studs. Unlike the sheathing elements

(with plate stiffness only), the beam elements retain all their DOF (3 DOF per node) thus

representing actual studs. The beam elements use the same nodes as the sheathing

elements except at geometrical intersections such as a wall-to-wall or a wall-to-floor

connection. The frame intersections (e.g. between sill plates and studs) are modeled as

pinned connections. The limitation of this shear wall model is the decoupling of in-plane

and out-of-plane responses. The other limitation is the hysteretic response of shear wall is

affected by boundary conditions. A small segment of an intersecting wall could increase

the shear wall’s capacity and ductility. However, it is not easy to determine the boundary

conditions. The authors thought the effect of boundary conditions may be more

significant at lower load and displacement levels while ultimate and post-ultimate

behavior may be less significantly influenced. Actually, based

Documents

DEVELOPMENT OF A GENERAL DYNAMIC HYSTERETIC …With some modifications on the nailed wood joint model, a super shear wall model was developed, which describes the behavior of a whole